The present invention relates to a tire valve unit that is used in a tire condition monitoring apparatus and has an appropriate securing structure by which the tire valve unit is secured to a rim of a wheel of a vehicle.
A tire condition monitoring apparatus of a vehicle is known. The device allows monitoring of the condition of the tires of the vehicle such as air pressure from the passenger compartment. Various types of tire valve units used in the tire condition monitoring apparatus have been proposed. One such tire valve unit typically includes a tire valve, an elastic cylindrical member, and a tire sensor. The tire valve has a valve body and a valve stem extending from the valve body. The valve stem is a hard cylindrical member formed of metal. The elastic cylindrical member is formed of, for example, rubber and encompasses the valve stem. The tire sensor is, for example, a air pressure sensor and installed in the elastic cylindrical member. The tire valve unit is secured to the rim of a wheel of the vehicle through the elastic cylindrical member.
This type of tire valve unit is described in, for example, Japanese Laid-Open Patent Publication No. 2001-174356. In the tire valve unit, an elastic cylindrical member encompasses the outer circumferential surface of a valve stem in such a manner that the elastic cylindrical member tightly contacts the outer circumferential surface of the valve stem. An annular securing groove, which extends circumferentially, is defined in the outer circumferential surface of the elastic cylindrical member. A tire valve is secured to the rim of a tire through snap-in attachment. Specifically, a portion (a securing portion) of the rim around the securing groove is fitted in the securing groove of the elastic cylindrical member. In this state, an engagement portion of a tire sensor is joined with an end of the elastic cylindrical member located inside the rim. The tire sensor is thus secured to the tire valve.
To secure the tire valve unit to the rim, the elastic cylindrical member must be held in a compressed state when being passed through a valve securing hole. However, the hard valve stem, which is arranged radially inward from the elastic cylindrical member, makes it difficult to compress the elastic cylindrical member in a radially inward direction. This hampers securing of the tire valve unit to the rim.
Further, the rim of a wheel of a vehicle, to which the tire valve unit is secured, receives great shock or vibration caused by traveling of the vehicle. Therefore, to prevent the tire valve unit from separating from the rim and improve sealing performance between the tire valve unit and the rim, the tire valve unit must be reliably secured to the rim.